The Immortal Life Cycle of Turritopsis - http://8e.devbio.com/preview...
"The solitary medusa of this species can revert to its polyp stage after becoming sexually mature (Bavestrello et al., 1992; Piraino et al., 1996). In the laboratory, 100% of these medusae regularly undergo this change. Thus, it is possible that organismic death does not occur in this species!" - Sanjeev Singh